Project New Horizon

Executive Overview

Project New Horizon is a 5 MW / 50 MWh iron flow battery energy storage project under development at Salt River Project's (SRP) Copper Crossing Energy and Research Center in Florence, Arizona, developed by ESS Tech under a 10-year agreement with SRP. The system is designed to provide 10 hours of continuous discharge and is targeted for completion in December 2027, with design underway and manufacturing scheduled to begin in 2026. The project is co-located at Copper Crossing alongside a 99 MW flexible natural gas facility, a 55 MW utility-scale solar project under construction, and CMBlu Energy's Desert Blume long-duration storage project. Project performance data will be monitored jointly by SRP, ESS, and the Electric Power Research Institute (EPRI).

How It Works & Differentiation

ESS's iron flow battery uses iron, salt, and water as its core materials, circulating an iron-salt electrolyte through electrochemical cells that store and release energy via a reversible oxidation-reduction reaction. The system charges in 10 hours or less and carries a 25-year life expectancy, with over 90% domestic content and no risk of thermal runaway — characteristics that differentiate it from lithium-ion chemistry at long durations. At 10 hours of discharge, it addresses a storage window beyond the typical two-to-four hour range of lithium-ion systems, supporting multi-hour renewable smoothing and overnight load shifting. The system can operate across a wide range of temperatures, which is relevant for Arizona's extreme summer conditions.

Commercialization & Traction

SRP, which serves approximately 1.1 million customers across Arizona, has signed a 10-year energy storage agreement with ESS, providing a committed utility offtaker for the project. SRP's existing storage portfolio of nearly 1,300 MW — including 1,100 MW of battery storage across eight facilities and 200 MW of pumped hydro — demonstrates the utility's established capacity for integrating grid-scale storage, situating the iron flow project within a broader and active procurement programme. The EPRI monitoring partnership adds an independent technical validation layer that strengthens the project's credibility as a commercial reference deployment for iron flow at utility scale. No pricing terms have been publicly disclosed.

Scalability & Strategic Context

The Copper Crossing Research Center's multi-technology design — hosting iron flow, lithium-ion adjacent to solar, and a separate organic flow battery project — is structured explicitly as an evaluation platform, with SRP comparing long-duration storage technologies under real operating conditions on the same site. Successful performance by ESS's system here would provide operational data to support larger-scale procurement decisions by SRP and other utilities across the U.S. Southwest, where high solar penetration and summer peak demand create strong demand for multi-hour storage. ESS's domestic content profile and non-toxic chemistry also align with procurement preferences emerging from the Inflation Reduction Act and supply chain diversification priorities.